The present invention relates in general to a fluid pressure responsive vehicle brake apparatus and, more particularly, the invention relates to an actuating mechanism for such brake apparatus that provides easy assembly thereof and fast response to fluid pressure application.
The invention to be described hereinafter is particularly useful on tramway-type vehicles and will be described in such application although it is not intended to be limited thereto.
Prior to the present invention, brake apparatus of this general type were known and taught in German Pat. No. 1,680,381 and in U.S. Pat. No. 3,995,537, the disclosures of which are incorporated herein by reference.
German Pat. No. 1,680,381 teaches a brake apparatus wherein a working surface parallel to a pair of wedge working surfaces is arranged on the brake push or thrust rod. A reaction surface parallel to each wedge working surface is provided in the brake unit housing. Positioned intermediate these coacting and parallel surfaces are roller means. With this design, even though the wedge-shaped working surface on the push rod and the working surfaces provided in the brake unit housing may be machined, it was difficult to maintain the rolling means in proper working positions between such surfaces. Furthermore, this particular brake apparatus design was comparatively large and cumbersome because it was found that such working surfaces on the push rod and within the housing were of necessity a length equal to one half the length of the wedge surfaces.
Some of the above difficulties were overcome with the brake apparatus taught in U.S. Pat. No. 3,995,537. This brake unit provides in a common housing, the upper part of which is formed as a cylinder, a fluid pressure actuated piston and a push or thrust rod, both of which are axially movable and arranged in a plane which are substantially perpendicular to each other. The push rod contains a driver sleeve arranged thereon through which forces may be transmitted from the sleeve to the push rod. At each end of the driver sleeve, a working roller is rotatably journalled in the housing of the brake unit at each side of the push rod.
The piston has attached thereto a fork-shaped wedge element placed astraddle the push rod and the driver sleeve so that each of its legs will extend down between the working roller and the reaction roller. Each leg has a reaction surface in the axial direction of the piston and cooperating with the reaction roller in addition to the working surface which is inclined in relation to the former surface and cooperating with the working roller.
A piston return spring is positioned between the piston and a spring support on the driver sleeve. The spring support has a pin which extends through the sleeve and into the push rod with a rounded end therein so that the rotational connection between these two parts may be removed at the manual turning of the push rod by means of a nut.
A push rod return spring is arranged between the housing and the drive sleeve.
Each of the above described brake units have a common disadvantage in the complexity of assembly thereof which adds considerably to the cost and maintenance.